On September 5, 2017, Minami-soma city made a statement on the city’s radiation levels compared to 3 cities in West Japan, which has been reported in several newspapers. It’s important to comment on this study because the statement is intended to persuade the population to return to live there.
We are publishing comments on the articles below after having discussed with M. Ozawa of the citizen’s measurement group named the “Fukuichi Area Environmental Radiation Monitoring Project“. For English speaking readers, please refer to the article of Asahi Shimbun in English. For our arguments we refer to other articles published in other newspapers – Fukushima Minyu and Fukushima Minpo – which are only in Japanese.
Here are the locations of Minami-soma and the 3 other cities.
Here is the article of the Asahi Shimbun
Fukushima city shows radiation level is same as in west Japan
By SHINTARO EGAWA/ Staff Writer
September 5, 2017 at 18:10 JST
MINAMI-SOMA, Fukushima Prefecture–Radiation readings here on the Pacific coast north of the crippled Fukushima No. 1 nuclear power plant are almost identical to those of sample cities on the other side of Japan.
The Minami-Soma government initiated the survey and hopes the results of the dosimeter readings, released Sept. 4, will encourage more evacuees to return to their home areas after they fled in the aftermath of the 2011 nuclear disaster.
A total of 100 portable dosimeters were handed out to 25 city employees from each of four cities–Minami-Soma, Tajimi in Gifu Prefecture, Fukuyama in Hiroshima Prefecture and Nanto in Toyama Prefecture. They were asked to take them wherever they went from May 29 through June 11.
The staff members were evenly dispersed with their homes in all corners of the cities they represented.
In addition, only those living in wooden houses were selected as different materials, concrete walls, for example, are more effective in blocking radiation.
In July 2016, evacuation orders for most parts of Minami-Soma were lifted, but not many residents have so far returned.
The city’s committee for health measures against radiation, which is made up of medical experts, analyzed the data.
The median value of the external radiation dosage of the 25 staff of Minami-Soma was 0.80 millisieverts per annum, while the average value was 0.82 mSv per annum, according to Masaharu Tsubokura, the head of the committee and a physician at Minami-Soma general hospital.
No significant difference was found in the three western cities.
Both figures were adjusted to include the natural radiation dose, and are below the 1-mSv per annum mark set by the national government as the acceptable amount of long-term additional radiation dosage, which is apart from natural radiation and medical radiation dosages.
The radiation doses in all cities were at levels that would not cause any health problems, according to Tsubokura.
“Making comparisons with other municipalities is important,” Tsubokura said. “I am intending to leave the survey results as an academic paper.”
1) The difference of life style between city employees and local agricultural population
As we see in the article, portable dosimeters were handed out to city employees. They spend most of their day time in an office protected by concrete walls which are efficient for blocking radiation as stated in the article. However, in Minami-soma, most of the population spends more time outside, very often working in the fields. Their life style is different and therefore the external radiation dose cannot be similar to those of city employees. The result of the comparison between the external radiation dose of city employees cannot be used as an argument to say that it is safe for the local population to live in Minami-soma.
2) In the article of Fukushima Minyu, it is stated that in Minami-soma the radiation dose has a wider range than in the other three cities. This means that there are hotspots, which leads to higher risks of internal irradiation.
3) The radiation dose expressed in terms of Sieverts is relevant for radioprotection when the source of radiation is fixed and identified. This is the case for most of the nuclear workers. However, in the case of Fukushima after the nuclear accident where the whole environment is radio-contaminated and the radioactive substances are dispersed widely everywhere, it is not a relevant reference for radioprotection. It is important in this case to measure surface contamination density, especially of soil.
4) 6 years and 6 months since the accident, cesium has sunk in the soil. It is thought to be between 6 and 10 cm from the surface. This means the top layer of soil from 0 to 5 cm is blocking the radiation, reducing the measures of the effective dose. However, this does not mean that the population is protected from internal irradiation, since cesium can be re-scattered by many means, by digging or by flooding, for example.
5) The reliability of individual portable dosimeters has already been raised many times. This device is not adequate to capture the full 360° exposure in radio-contaminated environments as described in point 3 above.
6) In the article, it is stated that background radiation is included in the compared values, but it does not mention the actual background radiation measurements in the 4 cities.
The Table of Fukushima Minyu
Radiation dose of the 4 cities
Values include the background radiation dose
To summarize, the sample study group does not represent the overall population. The study doesn’t include the risks of internal radiation, for which the measurement of contaminated soil is indispensible. The dosimeters are not adequate to measure the full load of radio-contaminated environments. So, the research method is not adequate to draw the conclusion to say that it is safe for the population to return to live in Minami-soma.